1. Field of the Invention
The present invention relates to multicast service channels and a method for operating a multicast service using the channels.
2. Description of the Related Art
A multicast means a service mode in which one of subscribers accessed to a local area network (LAN) or Internet transmits information to specific subscribers and the specific subscribers propagates the same information to a plurality of subscribers in a bucket relay mode. Such a multicast service mode is distinguished from a single-cast service (or unicast) for providing information to a particular individual or a broadcast service (or group-call service) for providing information to an unspecified number of the general public.
A general packet radio service (GPRS) specification provides packet data services based on a related art global system for mobile communications (GSM) for providing multimedia services such as voices, images and data transmission. The GPRS specification defines the multicast service as follows.
The multicast service is a unidirectional point to multipoint (PTM) service in which a message (specific multicast data) is transmitted from a single source entity to a plurality of subscribers currently located within a geographical area. The message contains a group identifier indicating whether the message is of interest to all subscribers or to only a subset of subscribers belonging to a specific multicast group.
Multicast data transmission is performed within the specified delay, over one or more geographical areas as defined by the service requester. Repeated transmission is performed where applicable according to the schedule as defined/negotiated by the service requester. No knowledge of the instantaneous, actual “receive group” present within the given area at any point in time is available within the network.
The service request is changed depending on QOS (Quality of Service) and the size of the geographical area.
In the multicast service defined by the GPRS, neither authentication nor ciphering is performed. The multicast service receives multicast data anonymously without signalling for subscriber group identification or subscriber identification.
Meanwhile, the multicast service defined by the GPRS has been partially supplemented for universal mobile telecommunication system (UMTS) which is being developed by the European Telecommunication Standard Institute (ETSI).
The multicast service of the UMTS is distinguished from the multicast service defined by the related art GPRS in that authentication and ciphering are available. Also, the multicast service of the UMTS is distinguished from the multicast service of the GPRS in that signalling for subscriber group identification or subscriber identification is performed to receive the multicast data anonymously or in its name.
In addition, the multicast service of the UMTS is less susceptible to transmission delay that depends on the radio environment. Moreover, the multicast service of the UMTS has a variable data transmission rate. That is to say, small data can be transmitted at low speed while large data can be transmitted at high speed.
The multicast service provided by the UMTS includes distribution services such as news, weather and traffic reports, as well as product or service advertisements, multimedia services such as audio, video and data, on-demand based high quality audio services, on-demand based video stream line services, and remote downloading services.
To classify various multicast services as described above, the UMTS uses subscriber group identification, or international mobile group identifier (IMGI). The IMGI is described in detail in the GPRS.
In other words, the IMGI can be used to identify specific subscriber groups defined by the GPRS such as the PTM groups. In more detail, the PTM groups are identified by the IMGI which supports both a provider identification level and an application identification level. Furthermore, the IMGI can be used to authenticate an individual subscriber as well as the groups.
The aforementioned related art multicast services are provided in an idle mode. That is to say, the user entities (UE) can receive multicast data only if they are in the idle mode. The UTRAN in the network provides the multicast services to the user entity groups located within its service area in the idle mode.
In the idle mode, a radio link control (RLC) layer establishes a radio link on a logical channel provided from a medium access control (MAC) layer which is a lower level than the RLC.
Therefore, since the related art multicast service is provided in a state that the radio link is only established between the UE and the UTRAN, the logical channel has been suggested as a multicast channel for a multicast signal (or data) transmission.
In more detail, in the IDLE mode, a transmission channel for data transmission service to a physical layer is not provided. In this case, a physical channel for interfacing the data transmitted to the transmission channel on the air after setting a call is not assigned.
For this reason, it is provided that a transmission channel such as a dedicated channel (DCH) or a forward access channel (FACH) temporarily used for other purpose is mapped with the multicast channel. However, the DCH is used for a connected mode that identifies a data unit for a specific service and transmits the data transmission service to the data unit. Therefore, the DCH is not assigned in the IDLE mode which is the basis of the multicast service. Also, since the forward access channel (FACH) provides slow power control to an up-link channel as the case may be, it is impossible to satisfy advantages of the multicast service of the UMTS having a variable transmission rate depending on the amount of data.
Accordingly, to achieve various multicast services in the future, new channels are required to efficiently transmit the multicast data. Efficient management plans of the multicast services are also required.